Combination of Pre-EGR Cooler Oxidation Catalyst and Water Vapor Condensation to Mitigate Fouling 2014-01-0636
Cooled exhaust gas recirculation (EGR) is widely used in diesel engines to control engine out NOx (oxides of nitrogen) emissions. A portion of the exhaust gases is re-circulated into the intake manifold of the engine after cooling it through a heat exchanger known as an EGR cooler. EGR cooler heat exchangers, however, tend to lose efficiency and have increased pressure drop as deposit forms on the heat exchanger surface due to transport of soot particles and condensing species to the cooler walls. In our previous work surface condensation of water vapor was shown to be successful in removing a significant portion of the accumulated deposit mass from various types of deposit layers typically encountered in EGR coolers. Significant removal of accumulated deposit mass was observed for “dry” soot only deposit layers, while little to no removal was observed for the deposit layers created at low coolant temperatures that consisted of both soot and condensed hydrocarbons (HC). The focus of this study was to explore the potential benefits of combining a pre-EGR cooler oxidation catalyst (OC) in the high pressure EGR loop with exposure to water vapor condensation. The catalyst oxidized close to 90% of inlet hydrocarbons at the conditions used in this study, thereby, preventing condensation in the EGR cooler downstream. Subsequent exposure to surface condensation of water vapor resulted in significant removal of deposit mass from these ‘dry’ soot only deposit layers. Addition of the oxidation catalyst in the high pressure EGR loop resulted in minimal additional pressure drop (< 2kPa) over the range of conditions tested in this study. Based on the findings in this study addition of a pre-EGR cooler oxidation catalyst to the high pressure EGR loop can offer several advantages such as mitigation of cooler fouling, expanded cooler operating range at the high hydrocarbon concentration points in the engine map and reduction in calibration complexity.